Concern for potential climate change resulting from the greenhouse effect may be the biggest factor in energy planning in the 1990s. A 20% reduction in CO2, the predominant greenhouse gas, has been proposed as a goal by several international and national groups. Its principal source is the combustion of fossil fuels. A substantial reduction in CO2 emissions in the first decade of the 21st century will require major shifts in energy planning and development in the 1990s. An energy systems model, MARKAL, is being used to identify cost-effective technological strategies to meet specific CO2 reduction goals. This can provide a technological basis for economic and policy models designed to find the best policy instruments to induce technological and behavioral change. This report focusses on MARKAL results in the electric supply sector.